The invention is directed to a safety device for electrical appliances, and particularly to a safety interlock mechanism for steam vaporizers which requires that a key, preferably one of the prongs of the power cord plug, be inserted into an opening in the vaporizer electrode assembly. While the use of a key other than the plug can circumvent the safety features, the use of the power cord plug as the key means, precludes its connection to a live electrical outlet, before the vaporizer electrode unit can be disassembled and reassembled.